Rod couplings are used to connect rods in downhole rod strings. The rods may be used for a variety of purposes, for example operating downhole pumps for pumping hydrocarbons to the surface. The rod couplings are usually wider than the rods, and since they typically reciprocate and/or rotate in the well, tend to wear against the casing or other material defining the well bore causing early failure of the casing, tubing or rod string. For this purpose, the rod couplings are usually coated with a rubber, urethane or elastomeric coating that prevents premature wear of the rod coupling. A difficulty arises in that the coating may be easily displaced on the rod coupling, thus ending its effectiveness, and causing the risk of the coating coming off the rod string and fouling equipment in the well. Knurling of the exterior surface of the rod coupling has been used to assist in adhering the coating to the rod coupling, and this helps to hold the coating on the rod coupling.
This invention is directed towards further securing the coating on a rod coupling. With the present invention, even if the coating wears through, it is less likely to detach from the rod coupling.